The invention relates to water purification.
Water must be effectively treated to remove or stop the growth of micro-organisms such as bacteria, parasites, or algae, particularly when the water is confined. Confined volumes of water are highly susceptible to rapid micro-organism growth and can become health hazards if not properly and regularly treated. Water purification can be accomplished by filtration or by treating the water with chlorine, bromine, ozone, or silver ions to provide water suitable for consumption or for use in recirculating systems such as swimming pools, hot tubs, spas, or cooling towers. For example, water can be treated with silver-containing materials described, for example, in U.S. Pat. No. 5,352,369 and in U.S. Ser. No. 08/628,405, filed Apr. 5, 1996 now U.S. Pat. No. 5,772,896 entitled "Self-Regulating Water Purification Composition" and filed Apr. 5, 1996, which are incorporated herein by reference.
In recent years, chlorine dioxide (ClO.sub.2 (g)) has been used to disinfect drinking water. See, for example, C. Yapijakis "R.sub.x for H.sub.2 O" Water & Water Engineering, May (1978), p. 33-37 and "Chlorine Dioxide" in Handbook of Chlorination and Alternative Disinfectants, G. C. White, Van Nostrand Reinhold, New York (1992), Chapter 12, p. 980-1045. Chlorine dioxide can be generated in several different ways. For example, chlorine dioxide can be produced by introducing chlorine gas into the flowing stream containing chlorite (ClO.sub.2.sup.-) or chlorate (ClO.sub.3.sup.-). Chlorine dioxide also can be produced by lowering the pH of a concentrated solution of chlorite or chlorate. This can be done either directly in water or, as in certain methods of disinfecting bandaged wounds, by adding an acid (e.g., citric acid) and water to a dry powder containing salts of chlorite or chlorate, as described, for example, in Chvapil et al. U.S. Pat. No. 5,104,660. Chlorine dioxide also can be generated by adding chlorine (HOCl) or exposing a catalyst to a solution containing chlorite. See, for example, Daly et al. U.S. Pat. No. 5,435,984.